My First Day Demonstration

Michael Morgan | Fri, 07/31/2015 - 19:23

I have a first day routine that I am very proud of. I have used it for 25 years and I think I finally have it down pat. I have spoken to students from 20 years ago at reunions and they tell me that they still remember the first day of chemistry so I think it is pretty good.

I start the class with a demonstration. Before the bell rings I try and spot a student I may already know or who at least looks like they can read out loud. I ask them if they are willing to read a short piece I have called “The Story of Ira Remsen “. Once this is set up I stand at the door and say hello to the kids and hustle them into the room. Once the bell rings, we begin. No introduction of who I am or what class it is. The first words out of my mouth are “We have a lot to accomplish this year and need to start now”. At that cue the student picked out earlier stands up and begins reading the paper I have given them.

You can read the script down below at the end of this entry. The set up for the demonstration is pictured in the cover photo for this entry. I start with a 1.0 L round bottom flask fitted with a one hole rubber stopper. A glass bend is inserted into the stopper and a piece of Tygon tubing about 30-35 cm long runs into an 2.0 L Erlenmeyer flask (glass tubing works well also). The Erlenmeyer is filled with distilled water, a few drops of base, and some phenolphthalein to give a nice pink solution. You can adjust what type of glassware is used but the reaction flask must be sealed (round bottom or Erlenmeyer fitted with a one hole rubber stopper). The second flask should be larger and open to the atmosphere but covered with some plastic wrap to keep smells under control. I add “some” concentrated nitric acid to the round bottom, usually about 25 mLs, and then drop in two pieces of copper, pennies from before 1983 work, or just small pieces of copper sheets from the stockroom. I immediately place the rubber stopper into the round bottom and the formation of the NO2 causes a nice stream of bubbles to form in the receiving flask. The pink color disappears as the NO2 forms an acidic solution. Once the system stops bubbling, it begins to cool, and a vacuum forms in the round bottom and the contents of the receiving flask are pushed (remember science never sucks) back into the round bottom. This is a slow process and if you watch the tube between the two flasks closely you can see movement of the liquid. The copper (II) ion gives a very nice blue color in the round bottom and the pennies are gone!

I act out the demonstration as it is described (with a few improvements to safety) and have the kids watch. Students usually ask to feel the heat on the bottom of the round bottom. Once it is reacting I ask them to take out a piece of paper and draw a picture of the demonstration while I call them up to sign program cards. As each student walks by I ask them to take a look at the apparatus. It takes about five minutes for it to cool enough to cause the back flow and at some point I can act out like some drama queen my fear of it exploding. I then have the students draw a second picture of what it looks like.

This demonstration is “dramatic and striking” and it sticks with the kids. I can point out something from just about every chapter of the year that is illustrated in the demonstration. The pictures they draw become the first page of lecture notes for the year and I am always referring back to them. One important point that I make is that they should not use “fancy” terms to describe what is going on, only plain old everyday language that they understand. It provides a really nice opening to the year. Class discussion immediately following can go in many directions.

As a note of safety I would remind you that it is using concentrated nitric acid, it does produce some nasty smells I try to control with the plastic wrap, and will require some effort to dispose of properly. You should have baking soda close for spills and use full safety equipment. Goggles, lab coat, and gloves are necessary. But this also provides a good example for kids from day one that you expect them to practice safe science also.

As with any demonstration I am reminded of a phrase that Fred Juergens the full time lecture demonstrator at UW Madison taught me when I was working there in 1991, “Prior Practice Prevents Poor Presentation”. You should rehearse a demo like this over and over again to make sure your opening day is one to remember.

I know much has been written about this demonstration and even video is available of the reaction but seeing it up close and personal is still best in my opinion. I do think the up close video is a really great way to augment the discussion and serves as an “instant replay”/

The Story of Ira Remsen

“While reading a textbook on chemistry, I came upon the statement, ‘nitric acid acts upon copper.’ I was getting tired of reading such absurd stuff and I determined to see what this meant. Copper was more or less familiar to me, for copper cents were then in use. I had seen a bottle marked ‘nitric acid’ on a table in the doctor’s office where I was then ‘doing time!’ I did not know its peculiarities, but I was getting on and likely to learn. The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words ‘act upon’ meant. Then the statement, ‘nitric acid acts upon copper,’ would be something more than mere words. All was still. In the interest of knowledge I was even willing to sacrifice one of the few copper cents then in my possession. I put one of them on the table; opened the bottle marked ‘nitric acid’; poured some the liquid on the copper; and prepared to make an observation. But what was this wonderful thing which I beheld? The cent was already changed, and it was no small change either. A greenish blue liquid foamed and fumed over the cent and over the table. The air in the neighborhood of the performance became colored dark red. A great colored cloud arose. This was disagreeable and suffocating—how should I stop this? I tried to get rid of the objectionable mess by picking it up and throwing it out of the window, which I had meanwhile opened. I learned another fact—nitric acid not only acts upon copper but it acts upon fingers. The pain led to another unpremeditated experiment. I drew my fingers across my trousers and another fact was discovered. Nitric acid acts upon trousers. Taking everything into consideration, that was the most impressive and, relatively, probably the most costly experiment I have ever performed. It resulted in a desire on my part to learn more about that remarkable kind of action. Plainly the only way to learn about it was to see its results, to experiment, to work in a laboratory.”

Read Deanna Cullen's blog referencing this same demonstration. You can also watch a video from our subscriber section of ChemEd X which explains the reaction.

I tried a modified version (I skimped on the nitric acid and used only ~2 mL so that the reaction took less time) of this during the first week and have to say it was an excellent addition. I was able to catch early on students who were not recording detailed observations or leaving out the entire last half of the reaction and give feedback during the same class period. This should benefit them when they begin doing their own experiments in the near future.

I also have a short observations assignment I tie in with this the first week. I use that as the very first entry into a portfolio for the kids. It is nice to show them how much they progress in their writing skills. Glad you liked it!

Thank you for this, Michael! I used it in my first day this year after hearing your talk at BCCE and it went very well. I look forward to revisiting it throughout the year. I would like to note a couple of disposal considerations for teachers interested in trying this.

1. Unstoppering the flask following the demo should be done in a fume hood. While it appears that most of the NO2 dissolves during the flowback, after the stopper is removed I could visually see more brown gas form. I imagine this is due to a couple of things: decreased pressure allowing NO2 to come out of solution and any excess NO reacting with newly introduced oxygen to form more NO2.

Nice comments! What you saw is a really neat thing to talk about with the kids. A decent amount of NO gas is produced in the reaction. It is not water soluble and collects at the top of the flask. That is the reason the flask did not fill completel with water during the back flow! When you opened the flask it hit oxygen from the atmosphere and immediately converted to NO2. I really don't think the decreased presure allows much (if any) NO2 to escape. It is all from the reaction of the NO.

It is all the little things lke that that I truly love about this demonstration. You can talk about it for days on end.